The present invention relates to a honing device for treating the surface of photoreceptors used in xerographic printers. In particular, the invention relates to a device for maintaining the concentration of a honing slurry during rinsing of a photoreceptor substrate.
Xerographic printers, such as laser printers, employ a cylindrical photoreceptor, analogous to the film in a camera, having a charged surface. Monochromatic laser light is used to selectively discharge areas of the photoreceptor surface. That surface is then exposed to toner or dry ink which is attracted to either charged or discharged portions of the surface, depending on the system used. The toner or dry ink is then transferred to paper.
The high reflectivity of the cylindrical photoreceptor surface causes a defect known as "plywood." The high reflectivity causes improper reflection of laser light, resulting in unintentional discharges on the surface of the photoreceptor. These unintentional discharges form a pattern resembling the grain of plywood. (See, e.g., U.S. Pat. No. 5,215,853.) To protect against the undesirable light reflections causing plywood, photoreceptors are fabricated with a light-scattering surface. One method of creating such a surface is honing. (See, e.g., U.S. Pat. No. 5,096,792.)
In honing, the cylindrical photoreceptor substrate is placed in a honing booth and sprayed uniformly with a slurry of a liquid, often water, and solid particles or beads, often glass. The forcible spray dulls the surface of the photoreceptor, forming a light-scattering surface. The honing operation itself, however, may produce defects affecting print quality.
For reasons which are not entirely known, during the honing process, some glass beads penetrate the surface further than others and become lodged in the surface. If not removed, these glass beads prevent proper charging or discharging of the photoreceptor surface in the neighborhood of the impacted glass bead, resulting in black spots or deletions in print depending on the system used.
Usually a rinsing operation is performed after honing to rinse away remaining glass beads. It has been determined, however, that even a short delay in rinsing following honing causes a significant increase in the number of glass beads remaining embedded after rinsing. That is, the number of permanent defects caused by embedded glass beads is directly related to the time delay between honing and rinsing. Delays on the order of 11/2 to 2 minutes produce significant increases in, and an unacceptable number of defects.
The delay involved usually results from concern over adversely effecting the slurry concentration through introduction of the rinse liquid into the honing booth. Rinsing the photoreceptor substrate with water in the honing booth immediately following honing decreases the concentration of glass particles in the slurry because the rinse water is combined with the existing slurry, decreasing the particle to liquid ratio. Even slight changes in slurry concentration detrimentally effect subsequent honing operations. Yet removing the photoreceptor substrate from the honing booth before rinsing in order to protect against changes in slurry concentration introduces unacceptable delays prior to rinsing.
Previous methods of monitoring and maintaining slurry concentration while rinsing have been proposed using significant additional equipment and expense. For those reasons, close monitoring and adjustment of slurry concentration has proven undesirable.